Diagnostic and monitoring systems are being increasingly used in rail vehicle traffic, the diagnostic and monitoring systems detecting changes in the state of components and assemblies of the rail vehicle in order to detect defects in these components and assemblies. In particular in the case of bogies of rail vehicles, the detection of unacceptable states of wear is of particular interest in terms of operational safety.
DE 10 2006 001 540 B3, which forms a generic type with respect to claim 1, proposes a method for monitoring the state of bogies of a rail vehicle, in which method the wheels of the wheel sets of the bogies are rigidly connected by means of axles and have a conical wheel profile. In this context, the sinusoidal motion of at least one wheel set is monitored, the sinusoidal motion being based on the conical wheel profile of the wheels, and when the sinusoidal motion fails to occur a signal is generated indicating the occurrence of derailing of the wheel set.
However, this method merely permits derailing of wheel sets to be detected depending on whether a sinusoidal motion is present or not in the sense of a binary state because a sinusoidal motion which is present generates a characteristic periodic signal which is completely absent after derailing. However, as a result with the known method there is no possibility of an early warning based on the observation of a slow or creeping change in bogie parameters or the state of wear.
According to DE 100 20 521 B4, which forms the generic type with respect to claim 4, the oscillation behavior of at least one vehicle component of a rail vehicle is monitored. The method described in the document is based on the fact that individual vehicle components react to the excitation of oscillations during operation with natural oscillations with a defined frequency, amplitude and damping. By comparing the determined actual nature oscillation with the anticipated natural oscillation which is stored as a reference value, a changed oscillation behavior of the monitored vehicle component is inferred so that this changed oscillation behavior is related to any fault sources in order to implement onboard diagnostics of rail vehicles. In this context, a frequency parameter, amplitude parameter and/or damping parameter of a natural oscillation of the respective vehicle component is continuously monitored.
In other words, according to the known document, the vehicle component is subjected to a type of modal analysis, and modal parameters such as the natural frequency and damping are monitored in order to detect damage as part of onboard diagnostics. However, the known method evaluates time profiles of the measurement signals in an undifferentiated fashion. In particular, signals which are obtained with the method under completely different peripheral conditions such as, for example, different coefficient of friction conditions or sliding friction conditions are evaluated together. Accordingly, the characteristic values from the Fourrier transformation such as, for example, the values for the natural frequencies and the amplitude maximum values thereof, are subject to a relatively large degree of variation which makes unambiguous and reliable evaluation of the frequency responses more difficult.
A disadvantage of the known method is that the excitation spectrum of a rail vehicle during operation is different to such an extent that at any individual point in time it is unclear what proportion of the measured signal is at all made up by natural oscillations of the respective vehicle component. This is due to the fact that not every external excitation of a vehicle component necessarily leads to natural oscillation of the vehicle component or to oscillation at the respective natural frequency.
Last but not least, for reasons of cost, it is conceivable that not every vehicle component of an assembly which is composed from a plurality of vehicle components such as, for example a bogie with wheel sets and anti-rolling damper is assigned a separate sensor. If therefore such an assembly is equipped with just one sensor and the known onboard monitoring yields the result that the assembly has deviating natural frequency characteristic values, it remains unclear which vehicle component (wheels of the wheel sets, anti-rolling damper) of the assembly has a fault.